Just about every web site comment form I see (other than for web sites requiring registration to comment) asks for name [required], email [required, but will not be displayed] and web site [optional]. It doesn't matter what you put in the email field, so why ask? Just tradition?

7 Answers
7

Sometimes there is an option to be informed about replies and e-mail is a natural option for such situations. It may also come down to trust that people who leave comments provide correct addresses so that you know that somebody has already commented before. This way you do not need to rely only on IPs and cookies.

What is more, there are websites and services that let you create an account and claim comments left under the e-mail address you have registered with. Disqs does it, for example.

Are you suggesting that the email serves as a means of verifying identity? Sites which require registration are another matter.
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foosionApr 13 '11 at 18:08

1

It does not verify identity (at least not when there is not a link sent for comment verification) but provides a sort of light, additional layer for probable verification. Statistically, it may work at some level as there are people who will just put a correct e-mail address (like me). People who won't usually insert something random so at least you can be fairly sure that you recognize the same person when the same, correct e-mail address is provided.
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wssbckApr 13 '11 at 18:22

Maybe it will be needed for you to get contacted, maybe you will be sent an email when you get an answer to a question or sometimes you must be held responsible for what you've said if you break the rules of that forum/website. Or maybe a certain forum post can win a prize and how can you prove that it's yours if it weren't for your email address? :)

Yes, there is another thing I have not though about. Sometimes you need to confirm the comment you left by clicking a link sent to you afterwards.
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wssbckApr 13 '11 at 18:04

Must provide email is almost universal, contact and prizes are much less common. "Held responsible" doesn't work if anyone can provide a fake address.
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foosionApr 13 '11 at 18:04

Some websites don't require registration, but won't post a comment unless you click on an emailed link. I regard that as the same as registration.
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foosionApr 13 '11 at 18:05

This cannot be the same as registration as you have no exclusive control over your account. An account of sorts may be created internally in the system for every address that is not tied to an already registered account but it still works more like a "guest user".
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wssbckApr 13 '11 at 18:19

By "held responsible" I meant more something like getting a penalty on the forum (warning and ban) - and yes, that's not always working, but requiring an email might limit the amount of visitors planning to just break the rules (won't stop trolls or signature hunters but might stop some of the bots trying to fill the forum with useless information, especially if there's CAPTCHA involved) and although prizes are rare, they do exist; Java Ranch holds contest quite frequently, for instance.
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keikiApr 13 '11 at 20:08

A lot of the time, it wants to know you're a real person--whether that is for the sake of the other two answers to this question by Michal Gancarski and Keiki. Usually, with some amount of bot/spider capturing software on the webserver, fake e-mails can get flagged, such as on domain hosts, that help add that little bit of security.

Of course, it's much more likely that they use it for other reasons as stated by the authors I mentioned. That is, to know who has commented before, to verify through e-mail sending that you're a real person (even more reliable than what I mentioned above, which might only weed out less than 1% of bots that scrawl your site), etc.